Prior art processing of sewage and wastewater often involves handling large volumes of sewage and wastewater flow in a channel, in order to separate solid and agglomerated matter therein and comminute such matter. It employs means of various screening and shredding devices in combination, which are positioned in the wastewater flow within the channel.
U.S. Pat. No. 5,490,922 discloses a sewage water installation that has a discharge basin in which is arranged a screening unit linked to a back-and-forth movable cleaning carriage. The mesh screen unit is depicted schematically and includes a plurality of parallel spaced bars forming the screen. A cleaning car, which moves back and forth, is allocated to the mesh screen. If the mesh screen is longer, several cleaning cars can be provided. A preferred cleaning car is provided with teeth that are designed correspondingly and arranged to protrude between the screen bars of the mesh screen and is intended for cleaning between the screen bars.
U.S. Pat. No. 2,672,985 discloses a transverse linear screen extending across an influent channel that intercepts all solids too large to pass therethrough. The screen consists of a plurality of parallelly disposed U-shaped members, with the U-shaped portions extending towards the inflowing sewage, forming a series of slots of the screen. A comminuting unit is disposed in parallel spaced relationship and in close proximity with the screen surface to remove collected solid materials therefrom by means of a cutting cylinder having a rotable shaft to which a plurality of cutting cylinders and combs are secured. As the comminuting unit travels back and forth along the width of a single linear screen by means of a direct drive motor in engagement with a rack device, the teeth project into the U-shaped portion of the slot members so as to remove solids intercepted by the screen. More details may be seen in FIGS. 5, 9, 10, 11 and 12 of the patent.
In U.S. Pat. No. 5,833,152, a unitary comminuting system, adapted for wastewater channel use, is provided with devices, which include a single or dual semi-cylindrical-like sizing screen. Each has a circular rotating sweeping mechanism of interactive slotted comb bars or blades. It sweeps and clears lodged or agglomerated solids adhering to the outer convex circumference surface of the screen, disposed in parallelly spaced relationship with a twin shaft shredder device having two parallel shafts with shredder or grinder teeth along the length thereof that rotate in opposite senses. The unitary system of devices is positioned perpendicularly between the influent and effluent sides of the wastewater flow in a channel so that solids therein will encounter the convex surface of the semi-cylindrical-like sizing screens or the twin shaft shredder as the wastewater flows through the channel. Both the single or dual semi-cylindrical-like screen devices cause solids, which do not flow directly there through, to be forcefully swept from the outer convex surface of the sizing screen. This employs the separate rotating sweeping interactive blade mechanism into surrounding the wastewater flow, so as to cause and divert or direct the solids to flow toward or into the contiguous twin shaft shredder device. This is aided by circulating wastewater currents generated in the wastewater flow near the entrance to the twin shaft shredder. It is generated in part by the rotating sweeping interactive blades of the screening devices, whereupon the removed solids are channeled into the twin shaft shredder device along with the other wastewater and solids flow where they are reduced in particle size.
These prior art devices were crudely constructed, difficult and costly to install, because they provide coarse and incomplete particulate processing and unreliable systems subject to frequent maintenance.
In U.S. Pat. No. 4,919,346, a moving mesh conveyor-screen allows flow to pass through while it diverts the solids to an adjacent twin shaft grinder for reduction in a unitized system. This invention is subject to screen maintenance and effectiveness problems as well as cutting efficiency problems to be discussed below. Its invention was superceded by U.S. Pat. No. 5,505,388 design because the screen was ineffective at transporting solids during low flow conditions, subject to plastering of solid debris against the mesh screen surface, and breakage due to stretching caused by water pressure.
U.S. Pat. No. 5,505,388 is substantially identical to the above patent with the exception that the mesh-screen is wrapped around a sprocket to form a rotating drum like member. Again, the rotating screen acts to allow flow to pass through while diverting oversized solids to the adjacent grinder. The operation can be inefficient and maintenance prone, because unreduced solids can bypass the grinder and pass downstream not masticated and because there are gaps between the rotating screen and the cutters through which a percentage of the solids pass unreduced. Further, solids become embedded in the rotating mesh drum-like screen and eventually get back-flushed downstream unprocessed. Maintenance problems include the solids are trapped within the central portion of the drum-like screen requiring maintenance for cleaning. The screen wears due to abrasion against bottom grit in the channel. In contrast to the present invention, solids accumulating within the unit during power outages often require the unit to be manually cleared of debris before it can be restarted. Only approximately one quarter of the screen area is workable, as the part closest to the channel walls cannot effectively transport the solids, and the part in the back of the drum is not active. This results in a reduction in liquid handling capacity.
U.S. Pat. No. 5,061,380 discloses another grinder-diverting system. It utilizes multiple parallel shafts with substantially parallel disks mounted thereupon, which intermesh one with another. The disks all rotate in a direction towards a vertically disposed grinder mounted to one side. This invention use an excessive amount of disks, drives and seal components, and thus makes it extremely difficult to maintain. Solids such as wood can become lodged within the disks and present a blockage condition requiring manual removal.
None of the above inventions is output controlled by any filtering device to assure a high percentage of reduction. The above devices suffer from components in the flow, which are subject to failure, wear, inefficient operation, seal failure, mechanical drive failure.
Accordingly, from a review of the foregoing prior art, it can be readily appreciated that it is desirable to find a comminution and screen cleaning system, which is simple and cost effective in construction and having low maintenance requirements. It is also preferred to remain rugged, efficient and effective for cleaning large size matter from the surface of a sizing screen and subsequently comminuting such removed matter along with other matter contained in the flow of wastewater at all levels in a sewage channel to smaller particle sizes.